5 Acknowledgments Firstly, I would like to express my deepest gratitude to my parents. Without their love and support, all of this would not possible. I would like to thank my supervisor, Professor José Augusto Afonso, for the help, patience and guidance, which was essential for the accomplishment of this thesis. I would also like to thank all my friends that, in one way or another, contributed for this work to be accomplished. iii

6

7 Abstract The emerging field of wireless body area networks (WBAN) has the potential to play an important role in everyday life, and there are many industries such as health, sports and entertainment that can take advantage of these networks. The wireless monitoring of users physical state, in indoor or outdoor environments, can bring benefits in several application scenarios; for example, it can increase patients general well-being and reduce caregivers workload by allowing continuous monitoring. This dissertation identifies and analyzes key performance aspects of using the ZigBee and IEEE protocols in WBAN applications. The main reason behind this work is because these protocols were designed primarily for wireless sensor networks (WSNs) but are also being used in WBAN applications, particularly in the healthcare area. The differences between WSN and WBANs are explained and are used to discuss the usage of the ZigBee and the IEEE standards in WBANs. The analysis performed in this work consists mainly in the execution of experimental tests with non-beacon enabled ZigBee/IEEE networks, using widespread hardware and software platforms from Texas Instruments, regarding relevant quality of service (QoS) metrics (maximum throughput, delivery ratio and network delay), as well as the effects of multiple constraints, such as hidden nodes, clock drift and body interference in the network performance. A clock drift model was proposed to estimate when two nodes will interfere with each other. This model was conceived due to the lack of support from the ZigBee to overcome this issue. A solution to overcome the clock drift and the hidden node problems was then designed. A parametric software delay model of ZigBee network devices was also defined and introduced into a simulator so that more accurate simulation results could be obtained. The proposed models were deemed valid since they were thoroughly tested and the predicted results were obtained. v

16 List of Figures. Figure Clock drift experiment test-bed in an anechoic chamber Figure Non-acknowledge IEEE associated times (a) and its minimum and maximum time boundaries (b) Figure Hidden-node experiment test-bed in an anechoic chamber Figure 3.15 HNPAvoidance application level virtual superframe structure Figure 3.16 HNPAvoidance application algorithm in the network coordinator Figure HNPAvoidance application algorithm in a network end device Figure VTS assignment sequence in the HNPAvoidance protocol Figure The sensor module and the communications module of a PMS device Figure Body interference experimental setup in an anechoic chamber Figure Body interference experimental setup in a classroom Figure 3.22 System Module and the Device model structures implemented with OMNeT Figure 3.23 Maximum theoretical and simulated goodput Figure 3.24 Delay components involved in packet transmission, in a packet relaying and in a packet reception Figure 4.1 Maximum goodput for star and 2-hop tree topologies Figure Delivery ratio measured with Z-Stack for an increasing number of sensor nodes transmitting in mode A Figure Delivery ratio measured with Z-Stack for an increasing number of sensor nodes transmitting in mode B Figure 4.4 Transmission model for tree topologies with Z-Stack Figure Delivery ratio measured with TIMAC for an increasing number of sensor nodes transmitting in mode A Figure Delivery ratio measured with TIMAC for an increasing number of sensor nodes transmitting in mode B Figure Average delay as a function of the number of sensor nodes transmitting in mode A for both Z-Stack and TIMAC Figure Maximum delay as a function of the number of sensor nodes transmitting in mode A for both Z-Stack and TIMAC Figure Maximum delay as a function of the number of sensor nodes transmitting in mode B for both Z-Stack and TIMAC Figure Delivery ratio using a 60 message window in a two hidden-nodes start topology in an anechoic chamber xiv

17 List of Figures. Figure Record of received packets in the hidden-node experiment in mode star_without_ack Figure Delivery ratio using a 60 message length window with two hidden nodes in a star topology Figure 4.13 Goodput measured and simulated for star and 2-hop tree topologies in mode Figure Delivery ratio measured and simulated for an increasing number of sensor nodes transmitting in mode A Figure Average delay measured and simulated for an increasing number of sensor nodes transmitting in mode A Figure Maximum delay measured and simulated for an increasing number of sensor nodes transmitting in mode A xv

25 Chapter 1 1 Introduction 1.1 Context Recent advances in the development of wireless communication and sensors for monitoring physiological signals are instigating the research in the field of Wireless Body Area Networks (WBAN), also commonly known as Body Sensor Networks (BSN). A BSN consists of a group of sensor devices distributed over the human body using a wireless network to support communications. New sensors have been developed to monitor many kinds of physiological parameters with great value for healthcare, performance evaluations of sport athletes or even in the entertainment business. In healthcare monitoring systems, BSNs can be used to collect and send signals obtained from the electroencephalogram (EEG), electrocardiogram (ECG), electromyogram (EMG), oximetry and other physiological parameters such as temperature or blood pressure. BSN-based monitoring can provide benefits in the diagnosis and treatment of patients without constraining their normal activities. It allows the patient to move freely inside or outside the hospital environment while providing continuous monitoring, which can be very useful when an extended period of monitoring is required. For example, many cardiac diseases are associated with episodic abnormalities such as transient surges in blood pressure or arrhythmias [Lo05]. These transient abnormalities cannot always be detected using conventional monitoring equipment. BSNs have the potential to provide early detection and prevention of pathologies, replacing expensive therapies later on. BSNs may be used in the sports sector to monitor the respiration rate or the athlete s movements to optimize their performances. For example, swimming athletes synchronize 1

26 Chapter 1. Introduction. their movements and respiration rate, which can be improved by analysing the data to correct imprecisions. BSNs are also being extensively used in the entertainment industry where users interact with video games using their movements, which are acquired through kinetic sensors. Every WBAN application usually has specific requirements and, due to this heterogeneity, a standard specification for the WBANs has not yet been published because to derive an all-in-one solution is very complex. The IEEE 802, an organization for the standardization of communication network protocols that proposed worldwide successful specifications such as the IEEE standards, established the Task Group IEEE , or IEEE TG6, for the standardization of WBANs. The main objective of the IEEE is to define new Physical (PHY) and Medium Access Control (MAC) layers for WBAN. This standard aims to include a network solution for both medical/healthcare and other non-medical applications with different requirements by supporting short range, lowcost, ultra-low power, high reliability and the coexistence of several applications into the same BSN for wireless communications in and around the body [IEEE6-08]. The MAC is the core protocol of any shared medium communication network. Thus, a suitable MAC layer is fundamental to fulfill WBAN requirements. In the Open Systems Interconnection (OSI) model, the MAC belongs to the first layer above the PHY layer and is used to coordinate the access of the nodes to the network communication medium. Its fundamental task is to avoid collisions, which have negative impact to the network performance. For WBAN systems, it has also the important task of providing Quality of Service (QoS) support to the applications, by controlling metrics like throughput efficiency, latency, communication reliability and energy efficiency. The MAC is one of the key layers regarding energy consumption in a WBAN because, since it acts upon the PHY layer, it can set the state of the nodes radio transceiver, which usually is the component that has the highest energy consumption rate in a low power sensor device. To reduce the energy consumption, the transceiver s state may be switched to sleeping mode, reducing the amount of energy wasted during idle periods. Typically, wireless MAC protocols are divided in two groups: contention-based or random access; and contention-free or scheduled access protocols. In contention-based MAC protocols such as Carrier Sense Multiple Access- Collision Avoidance (CSMA-CA), the nodes perform the Clear Channel Assessment (CCA) function to sense the channel before transmitting the data, in order to prevent collisions. Contention-free MAC protocols usually use techniques such as Time Division Multiple Access (TDMA) where packets may be transmitted into a time slot allocated to a particular 2

27 Chapter 1. Introduction. sensor node. Other medium access techniques like Code Division Multiple Access (CDMA) or Frequency Division Multiple Access (FDMA) are not suitable in the context of the wireless sensor networks (WSN) due to limitations in frequency spectrum availability and computation capability [Gopalan10]. The IEEE standard [IEEE4-03], particularly combined with the ZigBee protocol stack, is a widely adopted protocol in WSN applications, and is being used as an alternative for health care applications [Li09][López11]. The standard defines the PHY and MAC layers for low data rate, low power and low complexity short range radio frequency (RF) transmissions in a Wireless Personal Area Network (WPAN). The IEEE was originally designed for WSN, in which, usually, most of the supported applications generate low traffic loads to the network. Typically, WSN applications generate traffic only when triggered by external events, e.g., an out of range event detected through sensors (e.g. temperature or humidity). On the other hand, some BSN applications are data-intensive, generating a considerable amount of traffic due to high sampling rate requirements from some sensors. 1.2 Motivations and Objectives The IEEE WBAN standard is still in a development phase, where it is receiving several contributions from different manufactures in order to define the new specification. Meanwhile, the ZigBee/IEEE protocols already present several products in the market from multiple manufacturers and are currently being used in WBAN applications. Since the ZigBee/IEEE standards were not originally developed taking into consideration the specificities of WBAN applications, further analysis and revisions of these protocols are necessary, making this the main motivation for the development of the dissertation. The main objectives in this work are: To analyze the performance of non-beacon enabled ZigBee/IEEE networks in the context of WBAN applications, through experimental and simulation evaluations of relevant QoS metrics (maximum throughput, network delivery ratio (DR) and data delay), and the effects of multiple constraints, namely, hidden-nodes, clock drift effects and body interference; 3

28 Chapter 1. Introduction. To propose a solution to mitigate the hidden-node problem and clock drift effect in data-intensive WBANs with periodic traffic; To measure the software processing delay introduced by ZigBee/IEEE devices and to define and integrate a parametric model that takes into account this delay into a simulator. The experimental platform used to produce the results presented in this work was developed and tested using the ZigBee 2007 [ZigBee07] and IEEE implementations provided by Texas Instruments: the Z-Stack and the TIMAC, respectively. The hardware test platform is based on the CC2530 [TICC ] System on Chip (SoC) integrated circuit (IC), which is also provided by Texas Instruments. This SoC includes a microcontroller and a transceiver compatible with the IEEE standard, thus enabling the development of smaller sensor devices. The platform used in the simulations was the OMNeT++, which provides a simulation development environment based on discrete time events. It was used a software simulation model of the unslotted CSMA-CA of the IEEE protocol implemented by Pedro Macedo in his master s degree thesis [Macedo10]. 1.3 Contributions The main contributions of this work are: Experimental evaluation of the performance of ZigBee/IEEE networks in the context of WBAN applications. Results for the maximum throughput in a ZigBee sensor device; and the DR and delay for networks composed by up to 5 sensor devices transmitting to the coordinator in star and 2-hop tree topologies; are provided. Experimental evaluation based on the Packet Error Ratio (PER) and Received Signal Strength Indicator (RSSI) using a fully wireless WBAN system, regarding the interference of the human body in the radio communications; The definition of a model to predict the effect of the clock drift in the performance of data-intensive WBANs with periodic traffic; The proposal and implementation of an application level algorithm to solve the hidden-node problem (HNP): the HNP Avoidance protocol; 4

29 Chapter 1. Introduction. The definition of a parametric model to characterize the ZigBee/IEEE software processing delay and its integration into a simulator in order to obtain more accurate simulation results. 1.4 Thesis Organization This thesis is divided into five chapters, which are described as follows: Chapter 2 provides an overview of WBANs regarding the communication architectures and technologies that were used, as well as a description of WSNs based on the ZigBee/IEEE protocol, which includes these two protocols and other protocols of particular interest. This chapter also describes a kinetic monitoring system whose traffic parameters are used on the performance evaluations presented in this work. Chapter 3 describes the configurations adopted in the experimental tests that were executed to evaluate the performance of ZigBee networks when supporting data-intensive BSN applications. An introduction to the hardware that was used and a brief explanation of the programming environment are given. A number of QoS metrics are considered, and a connection from a theoretical standpoint to a more practical analysis is established. A model for software delay is proposed, and the simulator where it was implemented is described. The clock drift effect and a method to measure it are explained. The hidden node problem is discussed alongside with a protocol developed to solve this issue. Finally, the evaluation setup to a set of experiments regarding the body interference in the radio communications is provided. Chapter 4 presents the results obtained from the experimental component of this work, using the experimental evaluation scenarios and the proposed models detailed in the previous chapter. A series of graphs and tables are used to demonstrate the results from these experiments, which are commented and discussed Finally, chapter 5 presents the conclusions and indicates possible lines of future work for this research topic. 5

30

31 Chapter 2 2 Wireless Monitoring Overview This chapter provides some useful background information related to the topic presented in this work. An overview of wireless communications is given, covering body sensor networks, wireless sensor networks, and some protocols of particular interest, namely the IEEE and the ZigBee protocols. This chapter also presents a body sensor network applied to motion capture, the posture monitoring system (PMS), whose traffic parameters were used to acquire the results presented in this work. 2.1 Wireless Communications Wireless communications started in the late 19 th century when the wireless telegraph was created. Since then, wireless communications have evolved drastically; however, the foundation for most communication systems is still present, where radio waves are used for the transmission of information. The radio spectrum and wireless systems standardization are managed worldwide by the International Telecommunications Union (ITU) Radiocommunication Sector (ITU-R). Additionally, different national and regional agencies may be responsible for further regulations. Radio spectrum has several licensed frequency bands allocated to different communication technologies, e.g., radionavigation or terrestrial mobile communications. A group of license free bands were assigned to industrial, scientific and medical (ISM) applications [Akyildiz02]. These bands, known as ISM bands, are listed in Table 2.1. The main advantage of using the ISM bands is that they are license free, unlike the other bands that are allocated to particular paid communication services. On the other hand, 7

Wireless Physical Layer Q1. Is it possible to transmit a digital signal, e.g., coded as square wave as used inside a computer, using radio transmission without any loss? Why? It is not possible to transmit

Power Characterisation of a Zigbee Wireless Network in a Real Time Monitoring Application Arrian Prince-Pike A thesis submitted to Auckland University of Technology in fulfilment of the requirements for

ECGR-6185 Advanced Embedded Systems ZIGBEE 802.15.4 University of North Carolina-Charlotte Charlotte Chaitanya Misal Vamsee Krishna WPAN A personal area network (PAN) is a computer network used for communication

Multiple Access Techniques PROF. MICHAEL TSAI 2011/12/8 Multiple Access Scheme Allow many users to share simultaneously a finite amount of radio spectrum Need to be done without severe degradation of the

Wireless Personal Area Networks (WPANs) Bluetooth, ZigBee Contents Introduction to the IEEE 802 specification family Concept of ISM frequency band Comparison between different wireless technologies ( and

From reconfigurable transceivers to reconfigurable networks, part II: Cognitive radio networks Loreto Pescosolido Spectrum occupancy with current technologies Current wireless networks, operating in either

Local Area What s a LAN? A transmission system, usually private owned, very speedy and secure, covering a geographical area in the range of kilometres, comprising a shared transmission medium and a set

ZigBee A Case Study Copyright 2008 Cewidus Technologies Private Limited. All rights reserved. The information contained in this document represents the current view of Cewidus on the issue discussed as

Wireless LAN Concepts Wireless LAN technology is becoming increasingly popular for a wide variety of applications. After evaluating the technology, most users are convinced of its reliability, satisfied

ITU Kaleidoscope 2014 Living in a converged world - impossible without standards? An experimental test bed for the evaluation of the hidden terminal problems on the IEEE 802.15.5 standard David Rodenas-Herraiz,

Home and Building Automation Systems A SHORT INTRODUCTION A brief overview on home and building automation systems, with a particular focus on technologies, protocols and plant issues What? WHAT ARE THESE

Module 5 Broadcast Communication Networks Lesson 9 Cellular Telephone Networks Specific Instructional Objectives At the end of this lesson, the student will be able to: Explain the operation of Cellular

Remote Monitoring and Controlling System Based on ZigBee Networks Soyoung Hwang and Donghui Yu* Department of Multimedia Engineering, Catholic University of Pusan, South Korea {soyoung, dhyu}@cup.ac.kr

LoRaWAN What is it? A technical overview of LoRa and LoRaWAN Technical Marketing Workgroup 1.0 November 2015 TABLE OF CONTENTS 1. INTRODUCTION... 3 What is LoRa?... 3 Long Range (LoRa )... 3 2. Where does

Design and Performance Analysis of Building Monitoring System with Wireless Sensor Networks Mohammed A. Abdala & Alaa Mohammed Salih Department of Networks, College of Information Engineering, University

Wireless Ethernet LAN (WLAN) General 802.11a/802.11b/802.11g FAQ Q: What is a Wireless LAN (WLAN)? Q: What are the benefits of using a WLAN instead of a wired network connection? Q: Are Intel WLAN products

LoRa FAQs 1.) What is LoRa Modulation? LoRa (Long Range) is a modulation technique that provides significantly longer range than competing technologies. The modulation is based on spread-spectrum techniques

Wireless Medical Telemetry Laboratory 0 Introduction The development of wireless medical telemetry has become an increasingly popular application in recent years. As the elderly population continues to

I. The Healthcare Problem a. Explanation of why this solution is needed. b. How we can solve the problem. c. The components needed to solve the problem. II. Bluetooth Enabled Medical Device Architecture

Introduction Computer Network. Interconnected collection of autonomous computers that are able to exchange information No master/slave relationship between the computers in the network Data Communications.

Information Networks p. 1 CSMA/CA IEEE 802.11 standard for WLAN defines a distributed coordination function (DCF) for sharing access to the medium based on the CSMA/CA protocol Collision detection is not

Thingsquare Technology Thingsquare connects smartphone apps with things such as thermostats, light bulbs, and street lights. The devices have a programmable wireless chip that runs the Thingsquare firmware.

Maximizing Range and Battery Life in Low-Cost Wireless Networks The proliferation of cost-effective wireless technology has led to the rise of entirely new types of networks across a wide range of applications

THE BCS PROFESSIONAL EXAMINATIONS BCS Level 5 Diploma in IT October 2009 EXAMINERS' REPORT Computer Networks General Comments The responses to questions were of marginally better quality than April 2009

Department of Electrical and Computer Engineering Ben-Gurion University of the Negev LAB 1 - Introduction to USRP - 1-1 Introduction In this lab you will use software reconfigurable RF hardware from National

Wireless Local Area Networking (WLAN) Security Assessment And Countermeasures (IEEE 802.11 Wireless Networks) James Burrell Research project submission for the partial fulfillment of the requirements for

1 (1) Bluetooth voice and data performance in 802.11 DS WLAN environment Abstract In this document, the impact of a 20dBm 802.11 Direct-Sequence WLAN system on a 0dBm Bluetooth link is studied. A typical

Page 1 of 8 Computer Networking Networks 9.1 Local area network A local area network (LAN) is a network that connects computers and devices in a limited geographical area such as a home, school, office

To ensure the functioning of the site, we use cookies. We share information about your activities on the site with our partners and Google partners: social networks and companies engaged in advertising and web analytics. For more information, see the Privacy Policy and Google Privacy &amp Terms.
Your consent to our cookies if you continue to use this website.